Three-phase transformer



2 Sheets-Sheet 1 INVENTOR Pom/m0 D. A/fz SON April 9, 1946. R. D. NELSON THREE PHASE TRANSFORMER Filed May 17, 1945 I April 1946- R. D. NELSON 2,398,109

RRRRRRRRRRRRRRRRRRR ER Filed May 17, 1943 2 S heets-Sheet 2 INVENTOR. fuzz/m: a A/asm/ Patented Apr. 9, 1946 THREE -YPHASE TRANSFORMER Rolland D. Nelson, Hales Corners, Wis. acsignor to Line Material Company, South Milwaukee, Wis., a corporation of Delaware Application May 17, 1943, Serial No. 487,202

4 Claims.

This invention'relates to three phase transformers.

been made of the stacked core construction in -which a multitude 'of pieces of flat core steel were joined together by stacking to form the necessary shape of core for the three groups of conducting winding assemblies of the three phase transformer. This stacking operation entailed a high labor cost due to the long process of interleaving all of the small pieces of steel. It also required a relatively long and narrow shape of tank, the round tank being impractical to use with the customary type of core for the three phase transformer. These stacked types of three phase transformers were hard to repair in case of failure of one of the coils since it was necessary to remove the entire stacked end portion in order to remove the defective coil. Even in the initial stacking operation some mechanical stress was always imparted to the core pieces in the practical manufacture of the transformer and this reduced the efficiency of the transformer. Also in the stacked core construction it is necessary for the magnetic flux to travel cross grain at the corners of the core and this, in addition to the defect hereinabove noted, entailed a certain amount of loss in the core of the transformer.

This invention is designed to overcome the above noted defects, and objects of this invention are to provide a novel form of three phase transformer which has its core structure formed of wound magnetic ribbon, which is wound into closed cores, which are thereafter cut into sections and such sections used in the completed device, in which no unusual care is required in the assembly of the parts of the device, in which no bending, machining or other working of the core structure is required after annealing, and in which short-circuiting of the laminations is avoided.

Further objects of this invention are to provide a three phase transformer which in its preferred form is composed of cores which are formed of wound magnetic ribbon subsequently cut into sections and so arranged that an efficient three phase transformer core structure results, and in which the conducting windings may be very readily wound in a simple and ordinary manner upon the core sections without requiring any special machine other than the usual type of winding machines for winding the conducting windings.

This invention in its broadest aspect permits the use of stacked magnetic laminations or of wound cores formed of magnetic ribbon which are subsequently cut into parts after winding, the resulting magnetic core structure whether formed of stacked laminations or wound cores subsequently cut into sections being laminated throughout its entire extent.

Further objects are to provide a three phase transformer in which there are relatively few joints in the core structure, in which the joints in the core structure are so formed that a substantially edge to edge contact of the adjacent laminations is obtained, thereby materially reducing the reluctance of the magnetic path, and in which these results are obtained in a very simple manner and with a very small amount of work required in the manufacture of the device.

Further objects are to provide a novel construction of three phase transformers in which the losses are relatively small, and in which a very goodspace factor is obtained for the conducting winding.

Further objects are to provide a novel form of three phase transformer which is simple to manufacture and in which the number of operations required in its production is materially reduced.

Embodiments of the invention are shown in the accompanying drawings, in which:

Figure 1 is a plan view of the transformer with parts broken away and parts in section and showing in dotted outline the transformer cas- Figure 2 is an elevation of the transformer with parts broken away.

Figure 3 is a perspective view of the core structure.

Figure 4 is a plan view of a further form of transformer showing in dotted lines the outline of the transformer casing.

Figure 5 is an elevation of the transformer.

Figure 6 is a view of one of the core sections after it has had the conducting winding assembly wound thereon. I

Referring to the drawings, it will be seen that in the first form of the invention shown in Figures 1, 2 and 3, the transformer core structure comprises three identical core sections indicated by the reference characters I, 2 and 3. Each of these core sections is formed by winding a closed core of magnetic ribbon and cutting it across, preferably cutting it in half. The material used in making the cores is any suitable magnetic ribbon. It is preferable to use silicon steel, which may be either hot rolled or cold rolled, as this material has been found highly efficient in the manufacture of transformers.

As stated, the magnetic ribbon is wound to form a closed, continuous core and thereafter is cut across to form a pair of sections. These sections are arranged with their side faces in substantial contact. They may be in actual physical contact or they may be spaced apart by the oxide formed on the marginal edges of the laminations or by a layer of insulating paint or other insulating material that may be applied to the juxtaposed faces of the core section, or the insulation may be in the form of thin sheets between the end portions of adjacent core sections. It is preferable to grind the juxtaposed faces of these sections to get true, flat faces.

In the manufacture of the core sections, after the sections have been tightly wound as closed cores and cut, preferably in half, as described hereinabove, and after the appropriate faces have been ground, they are annealed while they are held in shape. After annealing no further working of the cores takes place in any manner whatsoever. Any wire edges that may be left are usually burned off during annealing, but if any should be found to remain, they may be removed by a wire brush or in any other suitable manner. After the core sections have been annealed, they are then separately wound to provide their primaries and secondaries, which will hereinafter be referred to as conducting winding assemblies, indicated respectively by the reference characters 4, 5 and 6. The windin is readily done in the ordinary manner on ordinary and common types of winding machines.

The core sections are then assembled as shown in Figures 1 and 2 and clamping means is provided for holding the sections clamped securely together. This clamping means may comprise a pair of upright angle irons l which are held in clamping relation by means of the upper and lower tie bolts 8. Insulating sheets 9 are positioned between the clamping means and the adjacent core sections to prevent short-circuiting across the ends of the core sections and it is preferable to provide an insulating sleeve indicated at ill on the tie bolts. It is to be noted that the tie bolt structure, that is to say, the bolt with the insulating sleeve l0, engages the upper and lower faces of the outermost layers of the core sections and thus prevent these layers from being distorted outwardly out of position.

It is to be noted particularly that the side edges of the adjacent laminations of the end portions of successive core sections are arranged in parallelism so that they have either an edge to edge contact or an edge to edge juxtaposition. By

having the edge to edge contact or edge to edge juxtaposition between the laminations of the central and outer cores, a material reduction in the reluctance of the magnetic path results.

It is to be noted that the magnetic flux travels lengthwise of the magnetic ribbon in substantially all portions of the core structure and this is the path having minimum magnetic reluctance. However, there is a small portion of the magnetic flux path where the flux travels crosswise of the magnetic ribbon where it passes from the end portions of one core section to the end portions of the adjacent core section. This path of cross travel of the flux is very short and is confined to a very limited portion of the entire flux path.

The invention may take other forms. For example as shown in Figures 4, 5 and 6, the cores may be wound out of magnetic ribbon to form closed cores as hereinbefore described and may be cut across into half sections with the cut extending across the cores at an angle to provide tapered or beveled end portions. The core sections are indicated by the reference characters I I, I2 and It in Figures 4 and 5. These sections are identical and the slanting or beveled face of one section indicated at I 4 is arranged either in actual physical contact with the side face of the adjacent section, as shown most clearly in Figure 4, or in close juxtaposition thereto. It is to be noted particularly that the edges of the adjacent laminations of the end portions of successive core sections are arranged in parallelism so that they either have an edge to edge contact or an edge to edge juxtaposition. By having the edge to edge contact or edge to edge juxtaposition between the laminations of the successive cores, a material reduction in the reluctance of the magnetic path results.

As stated, the magnetic ribbon is wound to form a closed, continuous core and thereafter is cut across to form a pair of sections. The cut or end faces of these sections and the juxtaposed side faces of the succeeding sections are preferably ground prior to annealing to get true, flat faces. These fiat faces may be in actual physical contact or they may be spaced apart by the oxide formed on the marginal edges of the laminations during annealing or by a layer of insulating paint or other suitable material that may be applied to the juxtaposed faces of the core sections or the insulation may be in the form of thin sheets between the end portions of adjacent core sections.

After the successive sections of the cores are formed by first tightly winding closed cores and thereafter cutting the wound cores into sections and are suitably ground as described above, they are annealed while they are held in shape, After annealing no further working of the cores takes place in any manner whatsoever. Any wire edges that may be left are usually burned off during annealing, but if any should he found to remain, they may be removed by a wire brush or in any other suitable manner. After the core sections have been annealed, they are then separately wound to provide their primaries and secondaries which are referred to as conducting winding assemblies and are indicated by the reference characters I 5, l6 and H, the winding being readily done in the ordinary manner on any of the common types of winding machines.

The core sections are then assembled as shown in Figures 4 and 5 and clamping means is provided for holding the sections clamped securely together. This clamping means may comprise three identical clamping means indicated generally by the reference character I8, each of which is provided with a pair of outwardly projecting ears I9 and with a single laterally projecting ear 20. They are positioned over the end portions of the successive core sections, as shown in Figures 4 and 5, and elongated tie bolts 2| are provided for drawing the ears 20 towards each other. Relatively shorter tie bolts 22 are provided for drawing the ears l9 towards each other. Suitable insulating sheets indicated by the reference character 23 are provided and positioned between the clamping members and their respective cores to prevent electrical short-circuiting of the laminations. It is to be noted that the clamping means not only holds the core sections together but also prevents the layers of the end portions from being distorted outwardly.

It is to be noted that the magnetic flux travels lengthwise of the magnetic ribbon in substantially all portions of the core structure and this is the path having minimum magnetic reluctance. However, there is a small portion of the magnetic flux path where the flux travels crosswise 01 the magnetic ribbon where it passes into the side edge portions of the adjacent laminations of succeeding core sections from the slanting end face of the preceding core section. This path of cross travel of the flux is very short andis confined to a very limited portion of the entire flux path.

It will be seen, therefore, that transformers have been provided by this invention which have a very small magnetic reluctance for the flux travel and which are extremely simple to make and which utilize the advantages of wound magnetic cores formed from magnetic ribbon though allowing the conducting winding assemblies to be wound in the ordinary simple manner without requiring any special processes or special machines. In winding the conducting winding assemblies', it is obvious that a core section can be placed in a lathe or other suitable machine and the conducting winding wound directly thereon in a very simple manner.

This invention, therefore, provides novel types of three phase transformer constructions which utilize the wound core rinciple but which nevertheless provide a very simple way of directly winding the conducting winding assemblies on each of the core sections.

It is to be noted further that the symmetrical arrangement of the core sections makes the transformer of either form 01 the invention fit readily within an ordinary cylindrical transformer casing as indicated by the dot and dash line of Figures 1 and 4, thereby having minimum lost space.

While it is much preferred to form the core sections in the manner hereinabove outlined, nevertheless it is to be understood that the core sections may be built up from laminations oi succeedingly greater lengths and shaped as shown in the drawings, and therefore it is to be understood that whenever the expressions laminations" or "magnetic laminations'are employed, it is intended that these expressions shall not be limited to stacked laminations but shall include any laminated structure whether it is formed by winding magnetic ribbon or by stacking magnetic laminations.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

1. A core construction for a three phase transformer comprising three separate symmetrically arranged core sections each being formed of magnetic laminations shaped to provide a main portion adapted to receive a conducting winding assembly and outwardly projecting end portions at opposite ends of the main portion, the end portions of thecore sections being in close juxtaposition and being cut across at an angle to their longitudinal axes to provide tapered, angularly shaped end portions, the end edges of the laminations of the angularly shaped end portions 01 each core section being arranged in close juxtaposition to, and in substantial alignment with, the side edges of the next adjacent core section.

2. A core construction for a three phase transformer comprising three separate, identical and symmetrically arranged core sections each being formed or magnetic laminations shaped to provide a main portion adapted to receive a conducting winding assembly and outwardly projecting end portions at opposite ends of the main portion, the end portions of the core sections being in close juxtaposition and being cut across at an angle to their longitudinal axes to provide tapered, angularly shaped end portions, the end edges of the laminations of the angularly shaped end portions of each core section being arranged in close juxtaposition to, and in substantial alignment with, the side edges of the next adjacent core section.

3. A core construction for a three phase transformer comprising three separate symmetrically arranged core sections each being formed of a part 0! a core wound from magnetic ribbon and cut across at an angle to provide a main portion adapted to receive a conducting winding assembly and outwardly projecting tapered end portions having slanting faces at opposite ends of the main portion, the end portions of the core sections being arranged in close juxtaposition, the end edges of the laminations at the slanting faces of the end portions f a core section being arranged in substantial parallelism with and in close juxtaposition to the side edges of the laminations of the next adjacent core section.

4. A core construction for. a three phase transformer comprising three separate symmetrically arranged core sections each being formed of a part of a core wound from magnetic ribbon and cut across at an angle to provide a main portion substantial edge-tome contact with the side edges or the lamination; oi the next adjacent core section,

ROLLAND D. NELSON. 

